Processing of substrates (e.g., semiconductor, glass, etc.) for use in electronic devices is typically done in one or more processing systems. Although multiple processing steps may be performed in a single processing system, substrates typically may be transported between processing systems for at least some of the processing steps.
Substrates generally are stored in cassettes or pods (hereinafter referred to collectively as “substrate carriers”) for transfer from one processing system to another, and between processing systems and other locations, such as storage locations. A substrate carrier may also be described in the art as a Front Opening Unified Pod (FOUP) or cassette. Each carrier may incorporate a plurality of ‘slots,’ or features designed to support a substrate in a pre-determined location, with suitable space between adjacent slots. Although substrate carriers may be carried manually between processing systems, the transfer of substrate carriers is typically automated. For instance, automatic handling of a substrate carrier may be performed by an automated material handling robot or vehicle, which may deliver and retrieve substrate carriers from a load port of a process tool, for example. The transfer robot or vehicle may be part of an Automated Material Handling System (AMHS). The contents of the substrate carrier are typically verified by “substrate mapping.” A need exists for improved methods and apparatus for substrate carrier content mapping.